Two types of optical connector ferrules have been described in Japanese Patent laid-open No. 63307409, the laid-open date of which is Dec. 15, 1988.
The first type of the optical connector ferrule comprises a ferrule body which is provided with a straight bore, and an auxiliary optical fiber which is fixed in the straight bore, such that the end surface of the auxiliary optical fiber is positioned at an intermediate portion of the straight bore.
In connecting two optical fiber cables, an optical fiber of one of the two optical fiber cables is inserted from one end of the ferrule body, at which the auxiliary optical fiber is not positioned, into the straight bore, such that the end surfaces of the auxiliary optical fiber and the inserted optical fiber face each other with an optical alignment in the straight bore. Thus, the inserted optical fiber is optically coupled to the auxiliary optical fiber by use of an optical matching (alignment) material which is filled into the straight bore before the insertion of the optical fiber, and is at least positioned between the end surfaces of the inserted optical fiber and the auxiliary optical fiber.
The second type of the optical connector ferrule comprises a pipe-shaped ferrule body, a glass capillary which is provided with a straight bore communicated through a slit at an intermediate portion to the external, and is fixed to be held in the ferrule body, and an auxiliary optical fiber which is fixed in the straight bore, such that the end surface of the auxiliary optical fiber is positioned not to extend beyond the slit.
In connecting two optical fiber cables, an optical fiber of one of the two optical fiber cables is inserted from one end of the ferrule body and then one end of the glass capillary, at which the auxiliary optical fiber is not positioned, into the straight bore, such that the end surfaces of the auxiliary optical fiber and the inserted optical fiber face each other with an optical alignment in the glass capillary. Thus, the auxiliary optical fiber and the inserted optical fiber are optically coupled to each other in the glass capillary by use of an optical matching material in the same manner as in the first type of the optical connector ferrule.
However, the first type of the optical connector ferrule has a disadvantage in that it is difficult to fill the optical matching material into the straight bore of the ferrule body without involving air in the optical matching material, because no air-escape means is provided in the ferrule body. Furthermore, the first type of the optical connector ferrule has a further disadvantage in that an optical fiber is pushed back to the inserting end of the ferrule body due to piston phenomenon, when the optical fiber is to be inserted into the ferrule, after the filling of the optical matching material is carried out, because an excess optical matching material can only escape through a clearance between the ferrule and the inserted optical fiber.
These disadvantages are overcome in the second type of the optical connector ferrule, because the glass capillary is provided with the slit functioning as an air-escape means and an optical matching material-escape means.
However, the second type of the optical connector ferrule has a disadvantage in that the optical matching material is liable to immerse between the inner surface of the straight bore of the glass capillary and the inserted optical fiber, thereby hindering the adhering of the inserted optical fiber to the inner surface thereof. If an optical matching material having an adhering property is used to avoid this disadvantage, an optical alignment of the inserted optical fiber and the auxiliary optical fiber is deteriorated, because the or flaking of the hardened optical matching material is liable to occur due to temperature change and a vibration thereof.